Optimization of retardance for a complete Stokes polarimeter.

We present two figures of merit based on singular value decomposition, which can be used to assess the noise immunity of a complete Stokes polarimeter. These are used to optimize a polarimeter featuring a rotatable retarder and a fixed polarizer. A retardance of 132 degrees (approximately three-eighths wave) and retarder orientation angles of +/-51.7 degrees and +/-15.1 degrees are found to be optimal when four measurements are used. Use of this retardance affords a factor-of-1.5 improvement in signal-to-noise ratio over systems employing a quarter-wave plate. A geometric means of visualizing the optimization process is discussed, and the advantages of the use of additional measurements are investigated. No advantage of using retarder orientation angles spaced uniformly through 360 degrees is found over repeated measurements made at the four retarder orientation angles.

Comparative craniofacial variation in Navajo Indians and North American Caucasians.

Landmarks digitized from lateral cephalometric radiographs of 107 Navajo Indians between 10 and 12 years of age were analyzed to determine coefficients of variation or standard deviations for 38 cephalometric measurements. These values were compared with the same measures of variation for identical measurements on North American whites derived from the Michigan and Philadelphia Growth Studies. For the majority of variables, there were no differences between groups. Variation for the genetically and environmentally isolated Navajo Indians was the same as that of the highly diverse Caucasian samples. However, measurements of upper, lower, and total anterior facial height (N-ANS, ANS-Me, and N-Me, respectively) indicate that these features are substantially less variable in Navajo Indians relative to the Michigan and Philadelphia populations.

Reprocessing of nonoptimally exposed holograms.

Two reprocessing techniques have been investigated that are capable of correcting the effects of nonoptimum optical density of photographic amplitude holograms recorded on Agfa-Gevaert type 10E75 plates. In some cases a reprocessed hologram will exhibit a diffraction efficiency even higher than that obtainable from a hologram exposed and processed to the optimum density. The SNR of the reprocessed holograms is much higher than that of the same holograms bleached with cupric bromide. In some cases the SNR approaches the optimum value for a properly exposed amplitude hologram. Subjective image quality and resolution of reprocessed hologram reconstructions appear to be no different than for normal single-development holograms. Repeated reprocessing is feasible and in some cases desirable as a means of increasing diffraction efficiency.

Measurement of diffraction efficiency, SNR, and resolution of single- and multiple-exposure amplitude and bleached holograms.

Five bleaching techniques for Agfa Gevaert Scientia 10E75 high-resolution plates were evaluated to determine resultant diffraction efficiency and SNR for identically recorded single-exposure holograms. We determined the optimum recording conditions for both single- and multiple-exposure bleached holograms using a cupric bromide bleach, judged to be the "best bleach." Data are presented for diffraction efficiency, SNR, and resolution of diffuse and focused-image holograms for both single- and multiple-exposure holograms, using a 1951 Air Force resolution chart as the object. Bleaching improved the diffraction efficiency of both types of holograms by up to 3 orders of magnitude. The SNR of diffuse holograms is degraded by bleaching, but that of the focused-image holograms is improved, while the resolution of both types is not affected by bleaching. Bleached multiple-exposure holograms are similar in response to single-exposure holograms except that their diffraction efficiencies are lower. The diffraction efficiency of bleached holograms decreases with age.

Holographic characteristics of 10E75 plates for single-and multiple-exposure holograms.

The holographic characteristics of Agfa-Gevaert Scientia 10E75 have been examined for multiple exposures. They include not only diffraction efficiency, but SNR and resolution as functions of number of exposures, time of development, and/or input modulation (rho'). The maximum diffraction efficiency, occurring at a density of 0.7, was observed to increase with increasing development time and decrease as the number of exposures increased. An approximately 10% decrease in maximum diffraction efficiency was observed for each successive reconstructed image of a multiple exposure hologram. Reconstructed noise was found to be fairly well represented by grain-noise considerations only for the region 0.1 < rho' < 0.4. Elsewhere noise is considerably different from grain-noise predictions. The SNR, at a density of 0.7, was observed to increase from 50 to 85 as the number of exposures increased from one to four. For postexposure or preexposure holograms the maximum signal-to-noise and resolution peaked near an input moduation of 0.4.